I. Field of Use
The present application relates to the field of energy management and control. More specifically, the present application relates to a robust communication protocol typically used in home networks that allow devices on the network to communicate with each other over long distances and in a noisy signal environment.
II. Description of the Related Art
Home automation has been around for many years, with a goal of monitoring and controlling various devices throughout the home. For example, the X10 protocol and associated devices have been around since 1978, offering remote control of appliances and lighting to consumers.
The X10 communication protocol uses either RF signals to communicate among devices in the network, or it uses powerline technology, which enables communication signals to be imparted onto standard AC power lines within buildings. An X10 protocol exists, which defines a data packet structure that allows data to be transmitted and received among devices. These data packets consist of a four bit identification code followed by one or more four bit unit codes, finally followed by a four bit command. For the convenience of users configuring a system, the four bit identification code is selected as a letter from A through P while the four bit unit code is a number 1 through 16.
When the system is installed, each controlled device is configured to respond to one of the 256 possible addresses (16 identification codes×16 unit codes); each device reacts to commands specifically addressed to it. For example, the protocol may transmit a message that says “select code A3”, followed by “turn on”, which commands unit “A3” to turn on its device.
While the X10 protocol provides many apparent benefits to consumers, there are numerous drawbacks related to the technology. For example, it is generally known that X10 is a relatively slow system, i.e., commands can take more than ⅓ of a second to send. This is too long for many applications, such as automated lighting, because humans—expecting an automated response—start to question whether the lights will come on at all after that amount of time.
Another disadvantage of X10's powerline communications is excessive attenuation of signals between two live conductors in 3-wire 120/240 volt systems used in typical North American residential construction. Signals from a transmitter on one live conductor may not propagate through the high impedance of the distribution transformer winding to the other live conductor. Often, there is simply no reliable path to allow the X10 signals to propagate from one transformer leg wire to the other; this failure may come and go as large 240 volt devices such as stoves or dryers are turned on and off. (When turned on, such devices provide a low-impedance bridge for the X10 signals between the two leg wires.) Often, active repeaters are necessary to amplify the signals as they traverse the network.
Yet still another problem with X10 is that RCDs (residual current devices) can attenuate X10 signals. These devices, commonly known as ground-fault interrupter (GFI) circuits, are electrical wiring devices that disconnect a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor. Such an imbalance is sometimes caused by current leakage through the body of a person who is grounded and accidentally touching the energized part of the circuit. A lethal shock can result from these conditions. RCDs are designed to disconnect quickly enough to prevent injury caused by such shocks.
All of the shortcomings of X10, taken as a whole, render communication between network devices generally unreliable and slow.
Another home control technology is known as Insteon; a system for connecting lighting switches and loads without extra wiring, similar to the X10 standard, designed specifically to address the inherent limitations in the X10 standard but also to incorporate backward compatibility with X10.
Insteon is designed to enable simple devices—such as light switches—to be networked together using powerlines, radio frequency (RF), or both. All Insteon devices are peers, meaning each device can transmit, receive, and repeat any message of the Insteon protocol, without requiring a master controller or routing software. The system is a dual-band mesh topology employing AC-power lines and a radio-frequency (RF) protocol to communicate with devices.
All Insteon powered devices act as repeaters, meaning that they repeat each message they hear. This is in contrast to other mesh networking topologies where only “advanced nodes” repeat. Automatic error detection and correction are included in all Insteon compatible products. The powerline protocol uses phase-shift keying and is designed so that the repetition is synchronized: all repeaters repeat the same message during precisely-defined time slots, so while the repetitions collide, they do so in harmony in a manner that preserves the message. The power line AC frequency is used as a synchronization source.
As with X10, powerline communication is not always dependable, and messages can be lost, even with an acknowledgment and retry scheme. Powerline communication reliability can be hampered by household appliances that generate electrical noise on frequencies near those used by Insteon communication (131.65 kHz). This makes it necessary to purchase additional products to repeat signals and filter noise.
It would be desirable to provide a home automation system that overcomes the limitations of the prior art.